With multiproduct formation of semiconductor products and short-living of a cycle time, a semiconductor production line is required to further shorten the TAT (Turn Around Time) and shorten the process processing time. With the trend toward an increase in the diameter of a semiconductor wafer (hereinafter simply called wafer), the weight per wafer is on the increase. Therefore, automatic processing of wafer conveyance by a machine becomes an essential requisite for a semiconductor production line that handles a wafer having a diameter of 300 mm.
In a semiconductor production line that accommodate a 300-mm wafer, the various manufacturing apparatus employed in the production are generally divided into equipment groups called bays, which in turn are disposed within a clean room in bay units. Therefore, a wafer automatic conveying system is also configured so as to be divided into elements (components), such as those related to bay-to-bay conveyance, those related to bay-in conveyance and stockers, correspondingly.
Of these components, a ceiling conveying method called an OHS (Over Head Shuttle) is generally used in the bay-to-bay conveyance. A conveying vehicle called a RGV (Rail Guided Vehicle) that automatically travels on a track, a conveying vehicle called an AGV (Automatic Guided Vehicle) that automatically travels on a non-track path, or an OHT (Over-Head Hoist transport) corresponding to one ceiling conveying method, or the like is used in the bay-in conveyance.
The stockers are disposed in relay locations between the bay-to-bay conveyance elements and the bay-in conveyance elements, respectively. Each wafer accommodated in the wafer conveying means (wafer carrier) is temporarily held in its corresponding stocker, after which it is conveyed into the bay. As the 300-mm wafer conveying means (wafer carrier), there is one which is called a FOUP (FOUP: Front Opening Unified Pod) wherein a wafer cassette and a pod (box) are unified to make it possible to convey a plurality of sheets of wafers in a sealed state, or there is another one which is called an open cassette (Open Cassette: OC) wherein a wafer is exposed in the clean room.
Incidentally, the wafer conveying system for a semiconductor production line that accommodates a 300-mm wafer has been described in “Monthly Semiconductor World”, Press Journal Inc., issued on Dec. 20, 1997, pp. 131–149.